Method of controlling load in mobile communication system by DTX period modification

ABSTRACT

The present invention relates to a method of controlling load in a mobile communication system in a system in which mobile stations include means for utilizing discontinuous transmission. In order to utilize the traffic capacity of the system more efficiently than before, at least one mobile station is equipped with regulation means for regulating its parameters related to discontinuous transmission, and a control signal is transmitted via a radio path to the at least one mobile station for regulating its parameters related to discontinuous transmission in such a manner that the mobile station transmits telecommunication signals to the other parts of the system more seldom or more often.

The present invention relates to a method of controlling load in amobile communication system in a system in which the mobile stationscomprise means for utilizing discontinuous transmission. The inventionfurther relates to a mobile communication system comprising a mobileexchange, base stations in a data transmission connection to the mobileexchange, and mobile stations in a radio connection to the basestations, said mobile stations comprising means for utilizingdiscontinuous transmission. The invention further relates to a mobilestation comprising transmission means and reception means for receivingand transmitting telecommunication signals via a radio path, a userinterface for receiving voice signals, and control means for utilizingdiscontinuous transmission, the control means comprising signalprocessing means for processing the voice signals received through theinterface by utilizing parameters stored in the mobile station fordetecting speech from the voice signals received through the interface.

The present invention relates to controlling the load in a mobilecommunication system in which the mobile stations can utilize DTX(Discontinuous Transmission). The GSM system (Global System for MobileCommunications) is an example of this sort of system.

Discontinuous transmission aims to prolong the life of a battery in amobile station by shortening the time a radio transmitter is in use.Furthermore, by reducing radio traffic, discontinuous transmissionreduces disturbing interference on a radio path. In order to achievethese objects, in discontinuous transmission a mobile station transmitsradio signals only when the user is speaking on it. In other words, thetransmission to the radio path is interrupted during the breaks inspeech. On the receiving side, pseudo noise, in other words comfortnoise, is generated during the breaks in speech when no speech framesare received from a radio path. The parameters describing backgroundnoise are computed on the transmitting side and transmitted to thereceiving side in the last frame, shortly before the transmission isinterrupted. In addition to this, they are transmitted at regularintervals in the signaling channel.

In the GSM system, a mobile station encodes speech in 20 ms sequences insuch a manner that a codec forms a set of parameters from each 20 msvoice sample. The size and structure of this parameter set is dependenton the codec used; there are several different codecs available. Totransmit speech in the GSM system is thus to transmit encoded blocks.

To ensure the utilization of discontinuous transmission, a mobilestation needs VAD (Voice Activity Detection) by means of which it can beexamined whether a particular voice signal comprises speech or merelybackground noise. A GSM mobile station utilizing discontinuoustransmission encodes speech at a rate of 13 kbit/s while the user isspeaking, and at other times (in other words when the user is notspeaking) at a rate of around 500 bit/s. The rate is sufficient fortransmitting background noise to the other party of the call in order tomake him/her notice that the call has not been disconnected.

There are various algorithms by means of which an encoded blockcomprising silence or background noise and a block comprising speech canbe discriminated from each other. Usually the algorithm used isdependent on the encoding method used. The aim is to select the DTXparameters in such a manner that speech and background noise could bereliably discriminated from each other. By regulating these parametersDTX can be made to function in such a manner that even extremely quietspeech can start a transmission or, on the contrary, a DTXparameterization by which a transmission is not easily started can beprovided.

The capacity of a mobile network is usually dimensioned in such a mannerthat the network is able to transmit the load peaks occurring normally.In other words, not every individual mobile station within the systemhas data transmission capacity continually reserved for it, but inconjunction with designing the network the aim has been to estimate themaximum capacity need, according to which the network has beendimensioned. In practice this means that mobile stations use existingdata transmission capacity alternately, and if the number ofsimultaneously active (a call is in progress) mobile stations exceedsthe number for which the capacity has been dimensioned, the mobilecommunication system fails to serve all mobile stations. Since it isextremely difficult to estimate the right capacity need in advance, inpractice situations occur in which the capacity of a mobilecommunication system runs out.

A way to ensure that the capacity of a mobile communication system issufficient is, of course, to increase the capacity of the network, inother words to dimension the network for a greater maximum capacity thanbefore. This, however, means increasing costs since in practice theresult would be an over-dimensioning in which the network would have tobe dimensioned for such a heavy traffic load which in practice wouldnever exist on it.

An object of the present invention is to provide a solution forcontrolling load in a mobile communication system in such a manner thatan existing traffic capacity can be utilized more efficiently thanbefore to make it possible to serve a larger number of mobile stationsthan before, without a need to increase the capacity of a network, whichwould increase equipment costs. This object is achieved with the methodof the invention, which is characterized in that at least one mobilestation is equipped with regulation means for regulating its parametersrelated to discontinuous transmission, and a control signal istransmitted via a radio path to at least one said mobile station forregulating its parameters related to discontinuous transmission in sucha manner that the mobile station transmits telecommunication signals tothe other parts of the system more seldom or more often than before.

The invention is based on the idea that when a control signal can betransmitted from a mobile network via a radio path to the mobilestations of the system, said control signal enabling the mobile stationsto regulate their parameters related to discontinuous transmission insuch a manner that the mobile stations less often transmit radio signalsto the other parts of the system, capacity can be released in thenetwork in such a manner that the number of the mobile stations whichcan be simultaneously served by the network increases. In other words,when it is noted that the load of the mobile network is approaching themaximum capacity of the network, the capacity in use can be released byordering the mobile stations to transmit more seldom than before,whereby a larger number of mobile stations can be served at a particularcapacity than before. In accordance with the invention, in somesituations the mobile stations can be similarly controlled to regulatetheir parameters related to discontinuous transmission in such a mannerthat the mobile stations transmit radio signals to the other parts ofthe system more often than before.

The most essential advantages of the method of the invention are that itenables the existing capacity of a mobile network to be utilized moreefficiently than before, that a larger number of mobile stations can beserved at the existing capacity than before, whereby equipment costsassociated with increasing the capacity are avoided, and that the methodof the invention can be applied to already existing mobile networks byextremely small changes, which can mainly be implemented by softwaremodifications.

The invention further relates to a mobile communication system in whichthe method of the invention can be applied. The system of the inventionis characterized in that the system comprises monitoring means formonitoring the traffic load in different parts of the system, controlmeans responsive to the monitoring means for transmitting apredetermined control signal to certain mobile stations or mobilestations located in a certain area via a radio path when the monitoringmeans indicate that the traffic load in some part of the system exceedsthe predetermined limit, and mobile stations comprising regulation meansfor regulating their parameters related to discontinuous transmission inresponse to the reception of the control signal in such a manner thatsaid mobile stations more seldom or more often transmit datacommunication signals to the other parts of the system.

An essential advantage is achieved particularly in a mobilecommunication system in which the data transmission connection between abase station and a mobile exchange is packet switched, when monitoringmeans are arranged to monitor at least the amount of the free trafficcapacity of the telecommunication connection between the base stationand the mobile exchange and to transmit a control signal to mobilestations communicating with the base station when the free capacitydrops beneath the limit value. In such a case, a reduction in the numberof speech frames transmitted by the mobile stations via a radio pathdirectly reduces the number of packets transmitted on the datatransmission connection, in other words the amount of free capacityincreases.

When the control means control the free traffic capacity of the radiochannels of a certain base station or alternatively the quality of acall transmitted via one or several predetermined base stations, thecontrol means detect when the load in a particular base station isbecoming too heavy. In the CDMA (Code Division Multiple Access) system,for example, this can be seen in transmission power exceeding a certainlimit. In such a case, an attempt can be made to release trafficcapacity in the area of the CDMA system in question by commanding themobile stations to transmit speech frames less often.

In a mobile communication system similar to the CDMA a radio interfacedoes not precisely restrict the number of calls taking place in the areaof one base station, but the calls have a practical limit, and to exceedthis limit leads to degraded voice quality of the calls. In this sort of“soft capacity” system, an attempt can be made to increase the capacity(by reducing interference) by the solution of the invention, whichreduces interference in a base station environment.

The invention further relates to a mobile station which can be utilizedin the system of the invention. The mobile station of the system ischaracterized in that the mobile station comprises detection means fordetecting a predetermined control signal received by reception means viaa radio path, and regulation means, responsive to the detection means,for changing said parameters utilized in speech detection by signalprocessing means in such a manner that the signal processing meansinterpret the voice signals received through a user interface asbackground noise more seldom than before or more often than before.

The preferred embodiments of the method and the mobile communicationsystem of the invention are disclosed in the attached dependent claims 2to 3 and 5 to 9.

The invention will be described in closer detail in the following by wayof example with reference to the attached figures, in which

FIGS. 1A and 1B illustrate the load in a mobile communication system,

FIG. 2 shows a flow diagram of a first preferred embodiment of themethod of the invention,

FIG. 3 shows a block diagram of a first preferred embodiment of themobile communication system of the invention,

FIG. 4 shows a block diagram of a preferred embodiment of the mobilestation of the invention, and

FIG. 5 illustrates the VAD function of the mobile station of FIG. 4.

FIGS. 1A and 1B illustrate the load in a mobile communication system.FIGS. 1A and 1B can be assumed to describe the load in a datatransmission connection between a single base station and a mobileexchange, for example, whereby the vertical axes describe load and thehorizontal axes time t. In FIGS. 1A and 1B, the allowed maximum load MAXis indicated by the horizontal line, whereby the total data transmissioncapacity available is in use.

FIG. 1A illustrates the load in a mobile network when the network isused by four mobile stations a to d. For the mobile stations, ahorizontal line is drawn when a mobile station transmits speech blocks.The figure shows that at time instant t0 all four mobile stationstransmit speech blocks simultaneously, whereby the load in the networkexceeds its maximum limit, in other words the network fails to serve allmobile stations without interference.

Similarly, FIG. 1B illustrates the load of the same mobile station as inthe case of FIG. 1A, but the method of the invention is applied to it,in other words, when the limit of the maximum load MAX of the network isapproaching, the network transmits a predetermined control signal to themobile stations to regulate the parameters related to theirdiscontinuous transmission in such a manner that the mobile stationstransmit speech frames less often than before. The load peak can thus bebalanced, and no overload similar to that in FIG. 1A occurs. For eachmobile station, the change in the number of speech frames to betransmitted can be very small indeed, but the regulation isall-important to the entire network (or a part of the network).

FIG. 2 shows a flow diagram of a first preferred embodiment of themethod of the invention.

In block A of FIG. 2 the load in different parts of the network ismonitored. Between a base station and a mobile exchange in a packetswitched transmission network, the number and/or size of the packets tobe transmitted can be monitored, for instance. In the radio interface ofa mobile network, the quality of connections in progress, for example,such as the bit error ratio, signal/noise ratio, or transmission powers(particularly in the CDMA systems) or corresponding parameters, whichhelp to form a picture of the interference level in a base stationenvironment, can be monitored.

In block B it is checked whether the load in some part of the mobilenetwork is heavier than the reference value Kmax determined for it.

In block C a control signal making the mobile stations regulate theirparameters related to discontinuous transmission in such a manner thatsaid mobile stations transmit speech frames less often than before, istransmitted to those mobile stations which utilize the part of thenetwork where the load exceeds the reference value Kmax. This can beachieved, for instance, by regulating those parameters which the mobilestations utilize for discriminating speech and background noise, wherebythe mobile stations interpret the voice signals received via theirmicrophones as background noise more easily than before.

In block D it is checked whether the load in a mobile network (in thesame part of the network in which the load in block B exceeded thereference value Kmax) drops below another reference value Kmin. If thisis the case, it means that the load peak of the network is passed, whichmeans a transfer to block E where a control signal making mobilestations regulate their parameters related to discontinuous transmissionto their initial values, is transmitted to said mobile stationsutilizing the part of the network in question.

As distinct from the block diagram in FIG. 2, the parameters related todiscontinuous transmission in mobile stations can also, of course, besteplessly regulated in such a manner that the regulation takes placesteplessly in response to the traffic load of a network.

FIG. 3 shows a block diagram of a first preferred embodiment of themobile communication system of the invention. It can be assumed by wayof example that the part of the mobile network shown in FIG. 3 is a partof the CDMA mobile network.

The mobile exchange MSC shown in FIG. 3 communicates with base stationcontrollers BSC1 and BSC2 via packet switched connections, and in thecase of FIG. 3, the base station controller BSC1 communicates with basestations BTS1 and BTS2 via packet switched connections L1 and L3.

In FIG. 3, the base station controller BSC1 is equipped with monitoringmeans 1 through which it monitors the load in the data transmissionconnections L1, L2 and L3. Furthermore, the base station controllermonitors the transmission powers of the mobile stations in the radiocells of the base stations BTS1 and BTS2 (in the CDMA system, thetransmission powers of a mobile station depend on the load in the radiocell in question). The monitoring means 1 thus note if some part of thenetwork becomes too heavily loaded.

When the monitoring means 1 detect that the load of the datatransmission connection L2, for example, is approaching its maximumallowed value, the monitoring means control the base stations BTS1 andBTS2 to transmit a predetermined control signal CNT to all mobilestations located in their radio coverage area. Said control signal ispreferably transmitted as a cell broadcast in some broadcast controlchannel, in which also other data intended to all mobile stations, suchas data on the calling channels of the radio cell, is transmitted. Thecontrol signal can thus be transmitted to the largest possible number ofmobile stations at the same time. Alternatively, the control signal canbe transmitted to each mobile station one by one by utilizing anexisting signaling channel.

In FIG. 3, mobile stations MS1 to MS5 utilize discontinuous transmissionin a manner known per se, in addition to which they are, in accordancewith the invention, equipped with regulation means for regulating theirparameters related to discontinuous transmission in response to the datacontained in the control signal CNT. Subsequent to said regulation, themobile stations MS1 to MS5 transmit speech blocks to the base stationsBTS1 and BTS2 less often than before, whereby the base stations BTS1 andBTS2 correspondingly strain the packet switched connection L2 betweenthe base station controller BSC1 and the mobile exchange MSC less thanbefore.

FIG. 4 shows a block diagram of the first preferred embodiment of themobile station of the invention. The mobile station in FIG. 4 can be aGSM system mobile station, for instance.

In FIG. 4, the parts related to discontinuous transmission are shown inblock TXDTX (Transmit DTX). From block TXDTX, speech frames, comprisinga flag SP (Speech) in the control bits which indicates whether saidframe comprises speech or whether a so called SID (Silence Descriptor)frame comprising data on background noise is in question, arecontinuously transmitted to the transmitting part. The SP flag isdetermined on the basis of a VAD flag provided from unit 2 indicatingspeech activity. When this flag has changed to zero, in other words whenspeech is no longer detected from the signal supplied from a userinterface 3 (from a microphone), the SP flag is also changed to zeroafter the number of frames needed for computing background noiseparameters, whereby a transmission unit TX still transmits the frameindicated by the zero flag and comprising the noise parameters to a basestation via a radio path. Subsequently, the transmitter TX stopstransmitting to the radio path, with the exception of the framecomprising noise data, transmitted at regular intervals. However, theTXDTX block continues to transmit frames comprising noise data to thetransmitter TX constantly.

When the VAD function redetects speech in the voice signal supplied fromthe user interface 3, the SP flag changes its value to one, whereby thetransmitter resumes continuous transmission.

In accordance with the invention, a detector 4 is arranged in the mobilestation in FIG. 4 for detecting the control signal received by areceiver RX and a regulation unit 5 which in response to the controlsignal detected by the detector 4 regulates the parameters used in theVAD function in response to the data in the control signal. Theparameters related to discontinuous transmission of the mobile stationin FIG. 4 can thus be regulated in such a manner that in conjunctionwith discontinuous transmission, the mobile station is made to interpretthe voice signals received from its user interface as background noisemore easily than before.

FIG. 5 illustrates the VAD (Voice Activity Detection) function of themobile station in FIG. 4. The VAD function is mainly based on thedetection of the energy of a signal received through a microphone. Inorder to eliminate background noise, however, the signal is filteredfirst, whereupon the energy of the filtered signal is compared with athreshold value, and if the threshold value is exceeded it is noted thatthe voice signal received through the microphone comprises speech.

The VAD function thus provides a plurality of alternatives for theinvention to be applied in such a manner that a mobile station can bemade to identify a received signal as background voice (and not asspeech) more easily than before. The method of the invention can thus beapplied by regulating the threshold value, for instance, oralternatively by changing the parameters of the filter, for instance.

The VAD function shown in FIG. 5 is described in detail in the GSMSpecification 06.32, which is incorporated herein by reference. Thespeech encoder of a mobile station computes the autocorrelationcoefficients ACF required by the GSM Specifications 6.10, saidcoefficients being supplied to the VAD function by the speech encoder.Similarly, to the VAD function is supplied a long term predictor lagvalue N obtained from the speech encoder of the GSM specifications 6.10.A VAD flag, which affects the value of the SP flag described inconjunction with FIG. 4, is obtained from the VAD function for initialdata.

It will be understood that the above description and the accompanyingfigures are only intended to illustrate the present invention. It willbe apparent to those skilled in the art that the invention can bemodified and varied in many ways without departing from the scope andspirit of the invention disclosed in the attached claims.

1. A mobile station comprising: transmission means and reception meansfor receiving and transmitting signals via a radio path; a userinterface with a microphone for receiving sound signals; control meansfor utilizing discontinuous transmission, whereby the control meanscomprises signal processing means for processing the sound signalsreceived through the microphone by utilizing filter parameters or athreshold value, which indicate how speech and background noise receivedvia the microphone should be discriminated, and which are stored in themobile station, in order to detect speech from the sound signalsreceived through the microphone; detection means for detecting apredetermined control signal received by the reception means via theradio path; and regulation means, responsive to the detection means, forchanging said filter parameters or said threshold value which indicatehow speech and background noise received via the microphone should bediscriminated and which are utilized in speech detection, in such amanner that the signal processing means interprets the sound signalsreceived through the user microphone as background noise more seldom ormore often.
 2. A mobile communication system comprising: a mobileexchange; base stations in a data transmission connection to the mobileexchange; monitoring means for monitoring load in different parts of thesystem; control means responsive to the monitoring means fortransmitting, via a radio path, a control signal to certain mobilestations or mobile stations in a certain area in order to regulatefilter parameters or a threshold value which the mobile stations utilizefor discriminating speech and background noise conveyed to a microphonein said mobile stations, when the monitoring means indicates thattraffic load in some part of the system exceeds a predetermined limit;and mobile stations in radio connection to the base stations, saidmobile stations comprising means for utilizing discontinuoustransmission, and regulation means for regulating said filter parametersor said threshold value which the mobile stations utilize fordiscriminating speech and background noise conveyed to the microphone inresponse to receiving the control signal, in such a manner that saidmobile stations interpret sound arriving at the microphone as backgroundnoise more often and transmit signals to the system more seldom.
 3. Amobile communication system as claimed in claim 2, wherein themonitoring means is arranged to monitor an amount of free trafficcapacity of the data transmission connection between at least one basestation and mobile exchange belonging to the system, whereby the controlmeans is arranged to transmit said control signal to all those mobilestations from which a traffic connection is in progress via said atleast one base station, when the control means indicates that the freetraffic capacity is below a predetermined limit value.
 4. A mobilecommunication system as claimed in claim 3, wherein said datatransmission connection between the base station and the mobile exchangeis a packet switched data transmission connection.
 5. A mobilecommunication system as claimed in claim 2, wherein the monitoring meansis arranged to monitor an amount of free traffic capacity of a certainbase station, whereby the control means is arranged to transmit saidcontrol signal to all those mobile stations from which a trafficconnection is in progress via said certain base station, when the freetraffic capacity is below a predetermined limit value.
 6. A mobilecommunication system as claimed in claim 2, wherein the monitoring meansis arranged to monitor quality of traffic channels of a certain basestation, whereby the control means is arranged to transmit said controlsignal to all those mobile stations from which a traffic connection isin progress via said certain base station, when the quality of thetraffic channels is below a predetermined limit.
 7. A method ofcontrolling the load in a mobile communication system in which at leastone mobile station includes means for utilizing discontinuoustransmission, comprising: monitoring traffic load in different parts ofthe mobile communication system, transmitting a control signal via aradio path to certain mobile stations or mobile stations in a certainarea in order to regulate filter parameters or a threshold value whichthe mobile stations utilize for discriminating speech and backgroundnoise conveyed to a microphone in said mobile stations, when trafficload in some parts of the system exceeds a predetermined limit; andregulating, by regulation means of said mobile stations as a response tosaid control signal, said filter parameters or said threshold valuewhich the mobile stations use for discriminating speech and backgroundnoise conveyed to the microphone in such a manner that the mobilestations interpret sound arriving at the microphone as background noisemore often and transmit signals to the system more seldom.